Solder fillers for aluminum body parts and methods of applying the same

ABSTRACT

One aspect of the present invention is a method of applying a solder filler to an aluminum body part. The method includes abrading the surface of an aluminum body part at a temperature of at least about 300 degrees Celsius with a solder filler at a temperature of at least about 300 degrees Celsius.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/063,300, entitled “Tin- And Zinc-Based Solder Fillers ForAluminum Body Parts And Methods Of Applying The Same” and filed on Apr.9, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One aspect of the present invention generally relates to solder fillersfor aluminum body parts and methods of applying the same, and morespecifically, to tin-based solder fillers for aluminum body parts andmethods of applying the same.

2. Background Art

Soldering processes are widely recognized and utilized within theautomotive industry. According to one definition, soldering is a processof joining metal body parts. The process typically includes treating themetal body surface with a filler material, otherwise referred to hereinas a body filler or body solder, to alloy with the parent metal, i.e.the metal body. In automotive applications, tin-based and zinc-basedbody solders are commonly utilized. The tin-based body solders are oftenapplied to metal body parts, such that an exchange of atoms, i.e.alloying, occurs at the interface between the applied body solder andthe metal body surface. Prior to soldering, one or more oxide layers ofthe parent metal are typically removed, or can be displaced viamechanical abrasion.

Aluminum alloys are finding an increased presence as a material in themanufacture of automobiles. The 5000 series of aluminum alloys are beingused more and more. Many of these alloys are characterized by theirsubstantial Mg content, i.e. greater than about 0.5 weight percent metalbody parts. Soldering aluminum alloys typically entails either (1) achemical reaction between a flux and the parent metal, to alter,dissolve, or remove the oxide layer, or (2) the mechanical break up ofoxide particles prior to the soldering step. Two basic types of fluxes,inorganic fluxes and organic-amine fluxes, are usually considered inconnection with aluminum body parts. Both have been successfully used inconnection with the soldering of certain aluminum body parts. However,these fluxes do have certain disadvantages. For example, inorganicfluxes used for the soldering or tinning of aluminum alloys can becorrosive before, during and after the soldering process. Moreover, theuse of inorganic fluxes typically includes the complete removal ofresidues after the pre-treatment step to ensure that minimal corrosiontakes place at a later time. The removal step can be time-consuming andexpensive. Although organic-amine fluxes are considered less corrosiveboth before and after soldering, they typically offer a relativelylimited active temperature range during heat cycling. Moreover, althoughremoval of organic-amine fluxes is often not necessary, these fluxes canalter the surface appearance of the aluminum after the soldering step.With both types of fluxes, fluoride fumes are usually generate duringthe heating cycle, and should be evacuated from work areas.

In light of the foregoing, fluxes based on current proposals for usewith certain aluminum alloys can be unsatisfactory, especially thosealuminum alloys containing greater than about 0.5% Mg. Moreover, a fluxdesigned specifically for the 5000 series of aluminum alloys has notbeen proposed. Engineering an effective flux for this type of alloy hasbeen hindered by the relatively high levels of Mg, a rapidly oxidizingelement. The levels of Mg are also relatively high in other lightweight, high strength aluminum alloys increasingly used for automotiveconstruction.

With respect to deoxifying via abrasion, body solders that contain zinc,including tin-based solders, are known to provide good mechanicalabrasion of aluminum while it is being heated, because of thesharp-edged, crystalline nature of basic Zn crystals. Even while in amolten state, zinc-containing alloys relatively quickly abrade anddissolve other metals with ease. However, the application ofzinc-containing alloys to aluminum body parts has been largelycommercially unsuccessful.

In certain soldering applications, a tinning step is used to providemore solderable coating than that of the untreated metal surface.Tinning can be described as a hot process for applying one or moresolderable coatings to base metals to form a true metallurgical bondbetween the two at the interface. Tinning can make subsequent solderingsteps more successful. To date, tinning processes for aluminum bodyparts have been largely unsatisfactory.

Body fillers are also needed in certain applications for joiningaluminum body seams. Current proposals for joining aluminum alloy bodypanels have been largely unsuccessful. For example, wetting 5000 seriesaluminum alloys followed by a relatively low temperature process has notbeen successful in forming a relatively strong metallurgical bond. Usingconventional high temperature processes on 5000 series aluminum alloys,for example inert atmosphere, vacuum brazing, or welding (e.g. laser)have been largely unsatisfactory.

By way of background, body fillers have been widely used in theautomotive industry to provide smooth and continuous surfaces bycovering and concealing surface imperfections such as spot welded jointsor body surface flaws. Numerous compositions have been used as bodyfillers for steel automotive body panels. For example, lead-containingbody fillers had been heavily utilized. Environmental concerns havecaused the automotive industry to move away from lead-containing fillersand focus on developing lead-free compositions.

Polymeric materials have been used as fillers. However, such materialsbond mechanically to the body part surface rather than metallurgically.The mechanical bonds are much weaker than metallurgical bonds. Inaddition, metallic components often must be added to the polymericmaterials in order to make the polymer conductive for electro-depositioncoating. Additionally, the polymeric material softening temperature istypically very close to the paint baking oven temperature. As a result,during the paint drying stage, the polymeric material can melt, thusdestroying the paint finish.

Body fillers have been proposed for aluminum automotive body panels, aswell. Some body solders fillers, thermally-sprayed solder fillers, andMIG-welded fillers used on steel panels have been unsuccessfully appliedto aluminum body parts. Many thermal sprayed and MIG welded fillercompositions for steel body parts have the potential to produce stresscracks and heat distortion when used with aluminum body panels. Thisdetrimental result occurs because the processing temperature requiredfor the steel solder filler is too high relative to the melting pointtemperatures of the aluminum alloys used in aluminum body panels.

Aluminum/silicon alloys have also been applied to aluminum pillar jointsusing MIG welding and thermal spraying techniques. However, theseapplication processes have the potential to produce stress cracks andheat distortion when used with aluminum body panels since the processingtemperature for the aluminum/silicon alloys is relatively close to themelting point temperatures typical of aluminum body panel alloys.

In light of the foregoing, it would be desirable to provide a method ofapplying solder fillers to aluminum body parts that provide favorablethermal and mechanical properties. It would also be desirable to providenew solder fillers for aluminum body parts and application methods thatprovide favorable thermal and mechanical properties, including theinhibition of stress cracking and heat distortion of the aluminum bodyparts.

These and other advantages will become more apparent to those ofordinary skill in the art upon reference to the following description.

SUMMARY OF THE INVENTION

One aspect of the present invention is a method of applying solderfillers to aluminum body parts that provide favorable thermal andmechanical properties. Another aspect of the present invention is solderfillers for aluminum body parts and application methods that providefavorable thermal and mechanical properties, including the inhibition ofstress cracking and heat distortion of the aluminum body parts.

According to a first embodiment of the present invention, a method ofapplying a solder filler to an aluminum body part is disclosed. Themethod includes abrading the surface of an aluminum body part at atemperature of at least about 300 degrees Celsius with a solder fillerat a temperature of at least about 300 degrees Celsius. The solderfiller can be a tin-based solder filler. The tin-based solder filler canconsists of, by weight, 55% to 85% Sn, 12% to 40% Zn, and 3% to 5% Ni,Fe, Cu or Co. The method can further include moving an instrument alongthe surface of the aluminum body part to remove a portion of the abradedsurface. The method can further include heating the surface to atemperature in the range of about 300 degrees Celsius to about 900degrees Celsius prior to the abrading step. The method can furtherinclude heating the tin-based solder filler to a temperature in therange of about 300 degrees Celsius to about 900 degrees Celsius prior tothe abrading step. In one embodiment, the tin-based solder filler canconsist by weight of 66.5% Sn, 30% Zn, and 3.5% Cu. In certainembodiments, the tin-based solder filler has a melting point in therange of about 195 degrees Celsius and 368 degrees Celsius. The aluminumbody part can be fabricated from a 5000 series aluminum alloy. Moreover,the aluminum body part can be fabricated of an aluminum alloy havinggreater than about 0.5% Mg.

According to another embodiment of the present invention, a method ofdeoxidizing an aluminum body part is disclosed. The method includesabrading the surface of an aluminum body part at a temperature of about300 degrees Celsius with a tin-based solder filler at a temperature ofat least about 300 degrees Celsius. The tin-based solder filler canconsist by weight of 66.5% Sn, 30% Zn, and 3.5% Cu. In certainembodiments, the abrading step is not preceded by a fluxing step.

According to another embodiment of the present invention, a method ofsoldering an aluminum body part is disclosed. The method includesabrading at least a portion of the surface of an aluminum body part witha tin-based solder filler consisting of, by weight, 55% to 85% Sn, 12%to 40% Zn, and 3% to 5% Ni, Fe, Cu or Co, applying a second solderfiller to a portion of the abraded surface portion, and heating thesecond solder filler to bond the solder filler to the aluminum bodypart. The second solder filler can be comprised by weight of about 95%Sn and about 5% Sb. In certain embodiments, the second solder filler hasa melting point in the range of about 232 degrees Celsius and about 240degrees Celsius. The applying step can include filling the abradedsurface portion. The applying step can include joining the abradedsurface portion to a second body part.

In another embodiment, a solder filler for aluminum body partsconsisting by weight of 81% to 85% Sn, 3% to 5% Zn, and 12% to 14% Cu isdisclosed.

In yet another embodiment, a solder filler for aluminum body partsconsisted by weight of 55% to 85% Sn, 12% to 40% Zn, and 3% to 5% Ni,Fe, Cu or Co is disclosed.

The above and other aspects and features of embodiments of the presentinvention are readily apparent from the following detailed descriptionof the best mode for carrying out the invention when taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may best be understood withreference to the following description, taken in connection with theaccompanying drawing which:

FIG. 1 is a melting point analysis of a tin-based alloy according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

As required, detailed embodiments of the present invention are disclosedherein. However, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. Therefore, specific functional details describedherein are not to be interpreted as limiting, but merely as arepresentative basis for the claims and/or as a representative basis forteaching one of ordinary skill in the art to variously employ thepresent invention.

In a first embodiment, before applying the solder filler to the aluminumbody part, a fluxing agent is applied to the aluminum body part. Heat isthen applied to the fluxing agent to deoxidize the surface of thealuminum body part. The solder filler is then applied to the deoxidizedsurface of the aluminum body part. The solder filler is usually producedin wire or rod form for application to the body part. After a fullheating cycle and soldering has occurred, the fluxing agent is renderedinert.

Preferably, a mixture of organic compounds and metallic salts is used asfluxing agents for the tin-based solder fillers. These fluxing agentsusually exhibit paste-like consistencies suitable for brush, spray andsyringe dispensing. Preferably, amines are used as a fluxing agent forthe tin-based alloy systems. It is understood that other fluxing agentsmay be used with the tin-based alloy systems as long as the agents canbe dispensed using a wide variety of techniques.

The preferable fluxing agents for the zinc-based alloy system is acombination of complex salts. These fluxing agents exhibit a paste-likeor slurry-like consistently suitable for brush, spray and syringedispensing. Preferably, complex organometallic salts are used as afluxing agent for the zinc-based alloy systems. It is understood thatother fluxing agents may be utilized with the zinc-based alloy systemsas long as the agents can be dispensed using a wide variety oftechniques.

In an alternative embodiment, the fluxing agent is mixed with one of thesolder fillers of the present invention to form a filler/flux mixture.For tin-based solder fillers, a mixture of 10% of fluxing agent and 90%of tin-based solder filler is prepared for the solder filler applicationprocess. For zinc-based solder fillers, a mixture of 50% of fluxingagent and 50% of zinc-based solder filler is prepared for the solderfiller application process. The fluxing agent can be mixed with powderedsolder filler to form a paste. The paste can be applied to the aluminumbody part through brushing, spraying, or syringe dispensing.Alternatively, the fluxing agent is injected into hollow solder fillerwire. The wire or rod is applied directly to the aluminum body part orit can be shaped into a preformed disk, ring, or tape or a contour closeto the filled surface for easy application. The filler/flux wire isparticularly suitable for filling in ditches or other blemishes on thesurface of an aluminum body part. It is understood that other mixingtechniques may be utilized that are consistent with the application of afiller material to an aluminum body part.

Once the solder filler or filler/flux mixture is applied to the aluminumbody part, heat is applied to bond the solder filler to the body part.Heat may be applied to the aluminum body part through the use ofconvective, conductive or radiant heat. A fuel gas flame or a plasmatorch may be utilized for heating. Flux residue is created by heatingthe filler/flux mixture. This residue is non-corrosive and can be easilywashed away during the normal cleaning, sanding and grinding carried outprior to painting the aluminum body part.

The final result of the final body filler application process is asmooth, continuous surface on aluminum body panels. It is understoodthat the application process may have to be repeated to build up theheight of the solder filler in cases of deep dents or ditches.

The present invention also includes several alloy compositions that areuseful as solder fillers for aluminum body parts. Two types of tin-basedsolder filler alloys are disclosed. A first preferred tin-based alloyincludes 12% to 22% copper, 3% to 5% zinc, and 73% to 85% tin. Morepreferably, the first preferred tin-based alloy consists of 20% copper,3% zinc, and 77% tin. A second preferred tin-based solder filler alloyincludes 3% to 5% copper, iron, cobalt or nickel, 12% to 40% zinc and55% to 85% tin. More preferably, the second preferred tin-based alloyconsists of 3.5% nickel, 30% zinc, and 66.5% tin. The tin-based alloycompositions contain other trace elements in order to provide a suitableviscosity for a solder filling material. Additionally, a zinc-basedsolder filler alloy is disclosed including a preferred composition of78% to 98% zinc and 2% to 22% aluminum. More preferably, the zinc-basedalloy consists of 80% zinc and 20% aluminum is utilized. In addition touse with aluminum body panels, the zinc-based alloys are also suitableas solder fillers for steel body parts.

The alloy compositions of this invention exhibit many desirableproperties. These properties are linked principally to the physicalproperties of the alloys. The tin-based solder filler alloys preferablyhave melting point temperatures ranging from 250 degrees Celsius to 350degrees Celsius and the zinc-based alloys preferably have melting pointtemperatures ranging from 400 degrees Celsius to 500 degrees Celsius.The melting point temperatures of the disclosed alloy compositions arepreferably at least 100 degrees Celsius lower than that of typical bodypanel aluminum alloys. The melting point temperatures for automobilebody panel made of aluminum alloys typically range from 620 degreesCelsius to 660 degrees Celsius. Consequently, the application of thedisclosed compositions inhibits stress cracking and heat distortion ofthe aluminum body parts. However, the melting points of the disclosedalloy compositions are high enough that the alloys remain solid in paintprocessing ovens. Additionally, the metallic nature of the disclosedalloys provide a solder exhibiting favorable thermal and electricalconductivity and satisfactory mechanical properties for electroniccoating processes. Moreover, the zinc-based alloys will not galvanizewith aluminum body parts.

According to another embodiment of the present invention, a method ofapplying a tin-based solder filler to an aluminum body part ispresented. This method is especially useful for pre-treating an aluminumbody part prior to soldering, e.g. filling and joining. In certainembodiments, the pre-treatment step includes abrading or swaging thesurface of the aluminum body part with a solder filler. In certainapplications, the aluminum body panel can be a 5000 series aluminumalloy, or other aluminum alloy having at least about 0.5 percent Mgcontent by weight. Advantageously, by use of this abrading step, thesoldering process does not have to include a fluxing step. The abradingstep can generate a metallurgically stable interface for the applicationof soldering materials.

In certain embodiments, the aluminum body part is heated to an elevatedtemperature range and is maintained in that temperature range during theabrading step. The temperature range can be within the range of about300 degrees Celsius and 900 degrees Celsius. One or more sources of heatcan be used to elevate and maintain the elevated temperature range.Using multiple sources of heat can deliver satisfactory volume anddistribution of the solder filler. In certain embodiments, the elevatedtemperature range is within the range of about 300 degrees Celsius andabout 450 degrees Celsius, which is considered to be a relatively lowtemperature range. This relatively low temperature range is often usedto join aluminum body parts since it offers certain advantages, forexample, reduction of stress cracking and warping. This range alsooffers relatively greater control of the heating process, and arelatively wide processing window, in which relatively safe forms ofheat can be utilized, for example, induction, infrared, hot air and/orcombinations thereof.

In certain embodiments, the solder filler is also heated to an elevatedtemperature range and is maintained in that temperature range during theabrading step. The temperature range can be within the range of about300 degrees Celsius and 900 degrees Celsius. In other embodiments, theelevated temperature range is with the larger range of about 300 degreesCelsius and about 450 degrees Celsius.

In certain applications, the solder filler can be a tin-based solderfiller, and more specifically, can include, by weight percent, 55% to85% Sn, 12% to 40% Zn, and 3% to 5% Ni, Fe, Cu or Co, although otheralloys may be used in accordance with embodiments of the presentinvention. In one embodiment, the tin-based solder filler consists, byweight, of 66.5% Sn, 30% Zn, and 3.5% Cu. In certain embodiments, atin-based solder filler having a melting point in the range of about 195degrees Celsius to about 368 degrees Celsius is suitable. FIG. 1 is amelting point analysis graph of the above-identified tin-based solderfiller. One of the reasons for using an alloy containing a certainamount of Zn is Zn metal's highly crystalline structure, which providesan effective abrading material.

Optionally, the abrading step can be followed by moving an instrumentalong the surface of the aluminum body part to remove residue formedduring the abrading step. This residue can contain oxidated materials.In certain embodiments, the moving step can be accomplished by scrapingthe surface of the aluminum body panel with a sharp instrument. Themoving step can occur after the abrading step is started, but before itconcludes.

According to one example, the aluminum body panel is a 5000 seriesaluminum body panel having greater than about 0.5% Mg content by weight,which is heated to a temperature of about 350 degrees Celsius. Atin-based solder material can also be heated to about 350 degreesCelsius prior to the abrading step. According to this example, thetin-based solder material can include, by weight percent, 55% to 85% Sn,12% to 40% Zn, and 3% to 5% Ni, Fe, Cu or Co. The heated tin-basedsolder material is then applied to the heated body panel, in a scrubbingmotion. By using an operating temperature of about 350 degrees Celsius,it has been found that the oxide layer of the aluminum body panel isnoticeably easier to scrape off than when the body panel is at roomtemperature.

Examples of uses for the fluxless abrading step include, but are notlimited to, filling ditches or imperfections in aluminum body panels togenerate a smooth, class-A metallic finish. Moreover, strips onuntreated aluminum body panels can be pre-tinned. The pre-tinned stripsare later folded to become hems prior to forming a finished part. Inother embodiments, after the fluxless abrading step, other panels can bejoined to the abraded aluminum body panel. For example, other panels andparts can be joined using sufficiently overlapping seams where themating surfaces of both parts have been previously abraded. In suchcircumstances, a second solder filler is selected for the joining step.Considerations for selecting the second solder filler can include, butare not limited to, strength and operating temperature range. In certainembodiments, a solder filler including by weight of about 95% Sn andabout 5% Sb is utilized. Advantageously, the second body filler materialcan wet to the abraded, i.e. tinned surface, for more easily than thatof the un-tinned surface. Selection of the second solder material mayresult in modifying certain characteristics of the finished joints. Suchcharacteristics may include ductility, strength, hardness, etc. Microstructure examination tensile tests and other methods may be employed toaid in matching alloys and solder fillers with complimentary heatingmethods to produce the best quality joints.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. A method of applying a solder filler to an aluminum body part, themethod comprising: abrading the surface of an aluminum body part at atemperature of at least about 300 degrees Celsius with a solder fillerat a temperature of at least about 300 degrees Celsius.
 2. The method ofclaim 1 wherein the solder filler is a tin-based solder filler.
 3. Themethod of claim 2 wherein the tin-based solder filler consists of, byweight, 55% to 85% Sn, 12% to 40% Zn, and 3% to 5% Ni, Fe, Cu or Co. 4.The method of claim 1 further comprising moving an instrument along thesurface of the aluminum body part to remove a portion of the abradedsurface.
 5. The method of claim 1 further comprising heating the surfaceto a temperature in the range of about 300 degrees Celsius to about 900degrees Celsius prior to the abrading step.
 6. The method of claim 2further comprising heating the tin-based solder filler to a temperaturein the range of about 300 Celsius to about 900 Celsius prior to theabrading step.
 7. The method of claim 3 wherein the tin-based solderfiller consists by weight of 66.5% Sn, 30% Zn, and 3.5% Cu.
 8. Themethod of claim 2 wherein the tin-based solder filler has a meltingpoint in the range of about 195 degrees Celsius and 368 degrees Celsius.9. The method of claim 1 wherein the aluminum body part is comprised ofa 5000 series aluminum alloy.
 10. The method of claim 1 wherein thealuminum body part is comprised of an aluminum alloy having greater thanabout 0.5% Mg.
 11. A method of deoxidizing an aluminum body part, themethod comprising: abrading the surface of an aluminum body part at atemperature of about 300 degrees Celsius with a tin-based solder fillerat a temperature of at least about 300 degrees Celsius.
 12. The methodof claim 11 wherein the tin-based solder filler consists by weight of66.5% Sn, 30% Zn, and 3.5% Cu.
 13. The method of claim 11 wherein theabrading step is not preceded by a fluxing step.
 14. A method ofsoldering an aluminum body part, the method comprising: abrading atleast a portion of the surface of an aluminum body part with a tin-basedsolder filler consisting of, by weight, 55% to 85% Sn, 12% to 40% Zn,and 3% to 5% Ni, Fe, Cu or Co; applying a second solder filler to aportion of the abraded surface portion; and heating the second solderfiller to bond the solder filler to the aluminum body part.
 15. Themethod of claim 14 wherein the second solder filler is comprised byweight of about 95% Sn and about 5% Sb.
 16. The method of claim 14wherein the second solder filler has a melting point in the range ofabout 232 degrees Celsius and about 240 degrees Celsius.
 17. The methodof claim 14 wherein the applying step includes filling the abradedsurface portion.
 18. The method of claim 14 wherein the applying stepincludes joining the abraded surface portion to a second body part. 19.A solder filler for aluminum body parts consisting by weight of 81% to85% Sn, 3% to 5% Zn, and 12% to 14% Cu.
 20. A solder filler for aluminumbody parts consisted by weight of 55% to 85% Sn, 12% to 40% Zn, and 3%to 5% Ni, Fe, Cu or Co.